43 research outputs found
Computational Study Of Diffuser Augmented Wind Turbine Using Actuator Disc Force Method
No full textIn this paper, a computational approach, based on the solution of Reynolds-averaged-Navier–Stokes (RANS) equations, to describe the flow within and around a diffuser augmented wind turbine (DAWT) is reported. In order to reduce the computational cost, the turbine is modeled as an actuator disc (AD) that imposes a resistance to the passage of the flow. The effect of the AD is modeled applying two body forces, upstream and downstream of the AD, such that they impose a desired pressure jump. Comparison with experiments carried out in similar conditions shows a good agreement suggesting that the adopted methodology is able to carefully reproduce real flow features
Multi-element ducts for ducted wind turbines: A numerical study
No full textMulti-element ducts are used to improve the aerodynamic performance of ducted wind turbines (DWTs). Steady-state, two-dimensional computational fluid dynamics (CFD) simulations are performed for a multi-element duct geometry consisting of a duct and a flap; the goal is to evaluate the effects on the aerodynamic performance of the radial gap length and the deflection angle of the flap. Solutions from inviscid and viscous flow calculations are compared. It is found that increasing the radial gap length results in an augmentation of the total thrust generated by the DWT, whereas a larger deflection angle has an opposite effect. Reasonable to good agreement is seen between the inviscid and viscous flow calculations, except for multi-element duct configurations characterized by large flap deflection angles. The viscous effects become stronger at large flap deflection angles, and the inviscid calculations are incapable of taking this phenomenon into account.</p
Ducted wind turbines: A potential energy shaper
No full textIn order to harvest wind resources more efficiently and to the greatest extent possible, unconventional wind turbine designs have been proposed, but never gained any acceptance in the marketplace. A team of researchers from TU Delft plans to revisit the concept of ducted wind turbines, which have been around for decades, and provide some clarity on its potential
Ducted wind turbines revisited: A computational study
No full textDucted Wind Turbines (DWTs) are one of the many concepts that have been proposed to improve the energy extraction from wind in comparison to bare wind turbines. In reviewing the DWT studies, investigations based on the combined use of theoretical, computational, and experimental techniques have been presented. Although indicated in these studies that the power output of wind turbines can be significantly increased by using surrounding ducts, the factors influencing this power increase, like the duct shape, augmentation add-on’s and yawed inflow conditions, need further investigation. These topics have been addressed in this doctoral thesis. The study presents a computational investigation of DWTs, employing two-dimensional and three-dimensional CFD simulations. To this intent, solutions obtained using panel, RANS, URANS and LB-VLES methods are shown. For reliable solution accuracy, verification and validation assessments are performed when possible. Through parametric investigation, it is found that the aerodynamic performance of the DWT can be improved by increasing the duct cross-section camber and a correct choice of turbine thrust force coefficient, whilst maintaining the same duct-exit-area ratio. The aerodynamic performance improvement for a DWT directly corresponds to the dimensionless duct thrust force coefficient. Flow analysis showed that flow separation when detected inside of the duct, reduces the duct thrust force coefficient and ultimately the aerodynamic performance of the DWT model. In an effort to further improve on the aerodynamic performance of the DWT, the effect of multi-element ducts and Gurney flap on the existing DWT models are investigated. The aerodynamic performance improvement with multi-element ducts strongly depends on the installation settings of the secondary duct element with respect to the primary DWT geometry. On the other hand, a Gurney flap retrofitted at the trailing edge of the duct improves the aerodynamic performance of the DWT model by delaying inner duct wall flow separation, thus increasing the mass flow rate at the turbine. Finally, the effects of yawed inflow condition on the aerodynamic and aeroacoustic performance of DWT models are studied in detail. The analysis showed that DWTs can demonstrate yaw insensitivity up to a specific yaw angle. The yaw insensitivity for the DWT model, however, strongly depends on the aerodynamic mutual interaction between the duct and turbine, which changes with the duct geometry, turbine configuration and yaw angle. While assessing the aeroacoustic performance of the DWT models, it is found that the DWT model xiii xiv Summary with highly cambered duct cross-section generates higher broadband noise levels, which results from the turbulent flow structures convecting along the surface of the duct.Wind Energ
Towards improving the aerodynamic performance of a ducted wind turbine: A numerical study
No full textThis paper aims to study the aerodynamic performance of ducted wind turbines (DWT) using inviscid and viscous flow calculations by accounting for the mutual interaction between the duct and the rotor. Two generalized duct cross section geometries are considered while the rotor is modelled as an actuator disc with constant thrust coefficient. The analysis shows the opportunity to significantly increase the overall aerodynamic performance of the DWT by a correct choice of the optimal rotor loading for a given duct geometry. Present results clearly indicate that the increased duct cross section camber leads to an improved performance for a DWT. Finally, some insights on the changes occurring to the performance coefficients are obtained through a detailed flow analysis
Ground effect for ducted wind turbines: A computational study
No full textDucted wind turbines (DWTs) can take the advantage of ground effect (GE) when installed close to urban areas. To this aim, a parametric study to investigate the aerodynamic performance of DWTs in relation to three different ground distances are investigated. The flow around a commercial DWT model using a simplified duct actuator disc (AD) model based on Reynolds Averaged Navier-Stokes (RANS) equations is performed. The results indicate that DWTs placed close to the ground will lead to increased mass flow rate the turbine plane, and thereby improving the aerodynamic performance. However, the additional ground force leads to an asymmetric flow-field at the turbine plane, which will ultimately induce unsteady forces on the DWT system. The present analysis will serve as a strong recommendation to address siting issues for DWT manufacturers. Team Jan-Willem van Wingerde
Uncertainty Quantification of A Wind Farm Control Model: FLORIDyn
No full textWind energy becomes more and more popular since it is environmentally friendly. Wind farm control is one of the most popular topics and it works on steering the wind farm to extract energy from wind as much as possible. Generally, the model capturing wake effects between turbines in the wind farm plays a role in wind farm control. The existing FLORIS model is considered suitable for wind farm control due to the fact that it has the ability or potential to capture wake features with reasonably computational costs. A drawback of the FLORIS model is the lack of dynamics, which is improved by developing the FLORIDyn model.This thesis focuses on a Gaussian FLORIDyn model. The objective is to explore the possibility of improving the model accuracy by quantifying the associated uncertainty in the model parameters. Uncertainty quantification consisting of sensitivity analysis and Bayesian calibration is conducted based on a 3-Turbine case simulation using the UQLab software. Since a MCMC algorithm associated with Bayesian calibration requires to evaluate the FLORIDyn model multiple times, it can result in massive computational expenses when directly applying the computational model to the simulation. To deal with this, a surrogate model is first constructed to replace the original model. This thesis assesses two types of approaches for surrogate model construction which are the Kriging-based approach and the PCE-based approach. One approach is chosen after the comprehensive comparison in terms of accuracy and efficiency. The constructed surrogate model is then applied to the sensitivity analysis using Sobol' indices to investigate how each model parameter of interest affects the model output. Last, the high-fidelity SOWFA data are used as experimental data for Bayesian calibration. Compared to non-calibrated model outputs, calibrated model outputs are closer to the SOWFA data, which means that the accuracy of the FLORIDyn model is improved.Mechanical Engineering | Systems and Contro
Effects of yawed inflow on the aerodynamic and aeroacoustic performance of ducted wind turbines
No full textDucted Wind Turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform inflows might be the cause of aerodynamic and acoustic performance degradation. For this reason, an aerodynamic and aeroacoustic analysis of DWTs in yawed inflow condition is performed for two duct geometries: a baseline commercial DWT model, DonQi®, and one with a duct having a higher cross-section camber with respect to the baseline, named DonQi D5. The latter has been obtained from a previous optimization study. A numerical investigation using Lattice-Boltzmann Very-Large-Eddy Simulations is presented. Data confirm that the aerodynamic performance improvement, i.e. increase of the power coefficient, is proportional to the increase of the duct thrust force coefficient. It is found that, placing the DWT at a yaw angle of 7.5°, the aerodynamic performances of the DonQi D5 DWT model are less affected by the yaw angle. On the other hand, this configuration shows an increase of broadband noise with respect to the baseline DonQi® one, both in non-yawed and yawed inflow conditions. This is associated to turbulent boundary layer trailing edge noise due to the turbulent flow structures developing along the surface of the duct.Wind Energ
Efficient Bayesian calibration of aerodynamic wind turbine models using surrogate modeling
No full textThis paper presents an efficient strategy for the Bayesian calibration of parameters of aerodynamic wind turbine models. The strategy relies on constructing a surrogate model (based on adaptive polynomial chaos expansions), which is used to perform both parameter selection using global sensitivity analysis and parameter calibration with Bayesian inference. The effectiveness of this approach is shown in two test cases: calibration of airfoil polars based on the measurements from the DanAero MW experiments, and calibration of five yaw model parameters based on measurements on the New MEXICO turbine in yawed conditions. In both cases, the calibrated models yield results much closer to the measurement data, and in addition they are equipped with an estimate of the uncertainty in the predictions
Characterization of aerodynamic performance of ducted wind turbines: A numerical study
No full textThe complex aerodynamic interactions between the rotor and the duct has to be accounted for the design of ducted wind turbines (DWTs). A numerical study to investigate the characteristics of flow around the DWT using a simplified duct–actuator disc (AD) model is carried out. Inviscid and viscous flow calculations are performed to understand the effects of the duct shape and variable AD loadings on the aerodynamic performance coefficients. The analysis shows that the overall aerodynamic performance of the DWT can be increased by increasing the duct cross-sectional camber. Finally, flow fields using viscous calculations are examined to interpret the effects of inner duct wall flow separation on the overall DWT performance.Wind Energ
